Infectious Bursal Disease (IBD), also known as Gumboro Disease, in poultry is caused by the Infectious Bursal Disease Virus (IBVD). The disease infects poultry worldwide and is responsible for large economic losses in the poultry industry. The disease causes diarrhea, muscular hemorrhages, inflammations, bleeding, damage to the immune system, and necrosis of the Bursa of fabricii and rectum. In infected poultry, the mortality is high and the surviving animals show retarded growth and insufficient feed utilization. Young animals 1-6 weeks old are particularly susceptible to the disease.
Several vaccines have been produced to control IBD. The IBDV has been isolated from the Bursa of fabricii and other organs in infected animals and used to produce live or inactivated viruses propagated in chicken embryos, newborn mice, or cultures containing bursa cells or chicken embryo cells. U.S. Pat. No. 3,548,055 discloses an IBD vaccine prepared from IBDV in which the virus was attenuated by passing the virus through at least eight consecutive passages in embryonic eggs. U.S. Pat. No. 3,769,400 discloses an IBD vaccine prepared from IBDV in which the virus was passed 18-25 times through immuno-suppressed baby mice. U.S. Pat. No. 4,530,831 discloses an IBD vaccine prepared by propagating an IBDV on chicken embryo fibroblast (CEF) cultures prepared from specific pathogen free (SPF) eggs. These vaccines, although not fatal, still produce some IBD symptoms in the vaccinated poultry, particularly gross and histological lesions on the Bursa of fabricii.
These prior art vaccines also share another common problem: the vaccines that can be administered to the animals by mass administration techniques remain sufficiently virulent to produce symptoms of the disease in the vaccinated animal, particularly necrosis or atrophy of the Bursa of fabricii; and the vaccines that have been attenuated to eliminate the symptoms of the disease when administered cannot be administered using mass administration techniques, these vaccines must be injected into each individual animal. Administering the vaccines through mass administration methods such as in drinking water or by spraying is simple, efficient, and not labor intensive. Injecting each animal is costly, time consuming, and labor intensive.
There exists, therefore, a continuing need for new and improved vaccines to combat IBD. There is a particular need for a vaccine containing an attenuated IBDV strain which can be administered using mass administration methods but which does not produce IBD symptoms in the vaccinated animal, particularly necrosis of the Bursa of fabricii.